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Re: [dinosaur] Dinosauria reclassification joins Ornithischia and Theropoda in Ornithoscelida



I'm not shocked or surprised. I've long been skeptical of the old saurischian/ornithischian divide and it's retention into the new century. Obviously Eoraptor for instance was an omnivore that could go in any direction. 

Not that the new division is definitive. The basal dinosaurs are just too anatomically basal to sort out what's really going on, and we may never know. 

If I do a 3rd edition of the field guide after the next turn of the decade it may be a real headache deciding what to do with this major phylotaxonomic question. 

GSPaul


-----Original Message-----
From: Ben Creisler <bcreisler@gmail.com>
To: dinosaur-l <dinosaur-l@usc.edu>; vrtpaleo-l <vrtpaleo-l@usc.edu>
Sent: Wed, Mar 22, 2017 2:13 pm
Subject: Dinosauria reclassification joins Ornithischia and Theropoda in Ornithoscelida


Ben Creisler

A new paper:

Matthew G. Baron, David B. Norman & Paul M. Barrett (2017)
A new hypothesis of dinosaur relationships and early dinosaur evolution.
Nature 543: 501–506 
doi:10.1038/nature21700


For 130 years, dinosaurs have been divided into two distinct clades—Ornithischia and Saurischia. Here we present a hypothesis for the phylogenetic relationships of the major dinosaurian groups that challenges the current consensus concerning early dinosaur evolution and highlights problematic aspects of current cladistic definitions. Our study has found a sister-group relationship between Ornithischia and Theropoda (united in the new clade Ornithoscelida), with Sauropodomorpha and Herrerasauridae (as the redefined Saurischia) forming its monophyletic outgroup. This new tree topology requires redefinition and rediagnosis of Dinosauria and the subsidiary dinosaurian clades. In addition, it forces re-evaluations of early dinosaur cladogenesis and character evolution, suggests that hypercarnivory was acquired independently in herrerasaurids and theropods, and offers an explanation for many of the anatomical features previously regarded as notable convergences between theropods and early ornithischians.

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Kevin Padian (2017)
Dividing the dinosaurs.
Nature 543: 494–495 
doi:10.1038/543494a

The standard dinosaur evolutionary tree has two key branches: the 'bird-hipped' Ornithischia and the 'reptile-hipped' Saurischia. A revised tree challenges many ideas about the relationships between dinosaur groups. See Article p.501


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